Preheat the oven to 350°F (175°C). Grease an 8-inch or 9-inch springform pan and line the bottom with parchment paper.
Whisk together the melted butter and granulated sugar. Add the eggs and vanilla and mix until smooth.
In a separate bowl, combine the flour, cocoa powder, and salt. Add the dry ingredients to the wet ingredients and stir just until combined. Fold in the chocolate chips.
Spread the brownie batter evenly into the prepared pan. Bake for 20 to 25 minutes, until the edges are set and the center remains slightly fudgy.
Let the brownie cool completely before adding the mousse.
Place the chocolate chips in a heatproof bowl. Heat 1/2 cup of the heavy cream until hot but not boiling. Pour it over the chocolate and let it sit for 1 to 2 minutes. Stir until smooth
Mix the cocoa powder, vanilla, and salt into the melted chocolate. Allow the mixture to cool until slightly warm or close to room temperature.
Whip the remaining 1 cup heavy cream with the powdered sugar until soft to medium peaks form.
Fold the whipped cream gently into the cooled chocolate mixture in two or three additions. Do not overmix.
Spread the mousse evenly over the cooled brownie base. Cover and refrigerate for at least 4 hours.
To make the caramel cream, whip the cold heavy cream, powdered sugar, and vanilla until soft peaks form. Gently fold in the caramel sauce and pinch of salt.
Drizzle with additional caramel sauce and garnish with chocolate shavings or mini marshmallows if desired.
Chill for another 30 to 60 minutes before slicing. For clean slices, use a sharp knife warmed in hot water and wiped dry between cuts.
